Neuroscientists now know that brain maturation continues far later into development than had been believed previously. Significant changes in brain anatomy and activity are still taking place during young adulthood, especially in prefrontal regions that are important for planning ahead, anticipating the future consequences of one’s decisions, controlling impulses, and comparing risk and reward. Indeed, some brain regions and systems do not reach full maturity until the early or mid-20s. Should this new knowledge prompt us to rethink where we draw legal boundaries between minors and adults?

Alas, age boundaries are drawn for mainly political reasons, not scientific ones.

Maybe, but it’s not as straightforward as it seems, for at least two reasons. First, different brain regions and systems mature along different timetables. There is no single age at which the adolescent brain becomes an adult brain. Systems responsible for logical reasoning mature by the time people are 16, but those involved in self-regulation are still developing in young adulthood. This is why 16-year-olds are just as competent as adults when it comes to granting informed medical consent, but still immature in ways that diminish their criminal responsibility, as the Supreme Court has noted in several recent cases. Using different ages for different legal boundaries seems odd, but it would make neuroscientific sense if we did it rationally.

Second, science has never had much of an influence on these sorts of decisions. If it did, we wouldn’t have ended up with a society that permits teenagers to drive before they can see R-rated movies on their own, or go to war before they can buy beer. Surely the maturity required to operate a car or face combat exceeds that required to handle sexy movies or drinking. Age boundaries are drawn for mainly political reasons, not scientific ones. It’s unlikely that brain science will have much of an impact on these thresholds, no matter what the science says.